Proper heating, ventilation, and air conditioning (HVAC) filtration is at the heart of indoor air quality. According to the United States Environmental Protection Agency, unfiltered indoor air is often significantly more polluted than outdoor air. Effective air filtration provides the primary defense against particulate and other pollutants not only to building occupants but also to the HVAC equipment and the building itself.
In large buildings, such as schools and office buildings, atmospheric air will be drawn into the HVAC system and passed through a series of filters disposed upstream of the HVAC system before reaching the occupied spaces of the building. The filters remove contaminants in the air flowing through the HVAC system. The efficiency of a filter determines the contaminants that can be removed by it. For instance, low-efficiency filters may be selected for removing lint and dust from air. Filters of medium and high efficiency can be selected to remove small particulates, such as bacteria, pollen, and soot.
Filters in large building applications are often disposed within filter banks. In filter banks, a filter holding frame holds each filter assembly, and the holding frames are fastened together to form an array of frames retaining an array of filter assemblies. The holding frames typically have sealing flanges extending around the inner periphery of the frame. Each sealing flange, potentially in cooperation with a gasket, abuts the filter assembly to limit the passage of unfiltered air around the filter assembly and through the HVAC system.
Within the filter bank, each filter assembly can include one or multiple filters. For instance, a first-stage filter, or pre-filter, can be retained in an outermost position in the filter assembly. Pre-filters are typically coarse, low-efficiency filters designed to remove large particles and debris. Such pre-filters protect not only building occupants but also the blowers and other mechanical components of the ventilation system from such large particles and debris, but pre-filters are not intended to be effective in removing smaller particles from the air. Instead, one or more secondary filters of higher efficiency must normally be disposed proximal to the pre-filter to remove small particulates.
Within the filter bank, filter assemblies are often retained within their respective holding frames by a plurality of spring clips. The clips can, for instance, be P-shaped spring clips with a loop of the P-shape sprung distally over the outer face of the filter assembly and the leg of the P-shape fastened to the holding frame. The spring clips are designed to tension the filter against the sealing flange of the holding frame. Where a pre-filter is to be used, a second spring clip normally must be used to mount the pre-filter to the filter and to the holding frame.
The need to use multiple, separate clips for final filters and pre-filters creates a cumbersome and mechanically complicated retention system. This is particularly true in the confined spaces with limited accessibility that are common to filter banks. Moreover, the need for plural clips for filters and pre-filters increases the risk of misapplication or malfunction and inadvertent displacement of the filter assembly thereby leading to an influx of raw air into the building structure. As a result, filters and pre-filters can be difficult and cumbersome to retain securely and to insert, remove, and replace. Filters that are difficult to install and handle are often less likely to be applied, tested, and maintained properly and are more prone to malfunction.
Meanwhile, preserving the operating efficiency and effectiveness of the filtration system and preventing failure requires that filters installed in the filter bank be inspected and replaced with suitable frequency. Replacement of a final filter becomes necessary when the resistance to air flow across the filter assembly, commonly measured as pressure drop, becomes unacceptably high. It will be further appreciated that pre-filters and coalescer elements often must be replaced three to four more tires more frequently than final filters. Filters pressed past their useful lives will eventually lead to excessive pressure drop. Pressure drop beyond design parameters overtaxes the HVAC system and risks filter failure and a resultant total loss in filtration.
Accordingly, being able to access, inspect, remove, and replace filters and pre-filters conveniently and efficiently is critical in the field of heating, ventilation, and air conditioning. Despite the filter clips and other retainers provided by the prior art, there remains a need in the art of heating, ventilation, and air conditioning and also in other fields where air filtration is required for a filter retaining mechanism that enables pre-filters and final filters to be retained securely and effectively while permitting filter 1 and replacement quickly and efficiently, ideally without a requirement for special tools.